1. Field of the Invention
The invention relates to a laser measuring device, in particular, which can maintain high responsivity irrespective of changes in surrounding environment, provide more correct measurement and long distance measurement due to reduced noise, and ensure the safety and reliability of a product.
2. Description of the Related Art
Space/object sensors for detecting three dimensional space and object can be divided into contact and non-contact sensors. Contact sensors are generally used in standard environments such as a factory, a building and an industrial site, whereas non-contact sensors can also be flexibly applied to non-standard environments in which various objects are measured.
Non-contact 3D space sensors are a device that acquires data, such as the distance to and the width and height of an object to be measured. The non-contact 3D space sensors radiate a sound wave such as a supersonic wave or a specific frequency of electromagnetic wave such as a laser beam and a Radio Frequency (RF) wave to the object in order to extract amplitude, (round trip) time, a phase value and so on from the wave refracting from the object.
Of these sensors, space sensors using the RF or supersonic wave are merely applicable to the recognition of a space in a short distance (several meters) owing to poor convergence and spatial resolution. That is, these sensors are generally used in limited fields, such as rear distance detection systems and cleaning robots. Conversely, sensors using a light source have merits, such as adjustable convergence, a high measuring speed, a high precision and a wide measuring range per unit time, and thus can be applied to various fields such as construction, military, autonomous mobile robots, topographic surveying systems and aerospace industry, which require the ability of measuring an object in a long distance (several kilometers) with a high resolution and a high speed.
The method of measuring the spatial distance to an object using a light source can be generally divided into triangulation, Time-Of-Flight (TOF) technology and interferometry.
The triangulation is a method of determining a spatial position of a specific point by analyzing a triangle, which are defined by the specific point and the other two points, the location information of which is already known. In the interferometry, that is, a measuring system using an interferometer, a beam is modulated into a predetermined frequency of sine wave, is radiated to an object, and is reflected from the object. The distance to the object is measured using the Optical Path Difference (OPD) between the reflected beam and the original beam, which is obtained when the beams are recombined after traveling along different optical paths. The TOF technology radiates a laser pulse into a space, detects a returning pulse using a light detecting device, and calculates the time difference between the radiation pulse and the returning pulse, thereby producing the distance to an object.
While the triangulation has excellent precision in short distance measurement, this method is not suitable for long distance measurement since a measurement error increases in proportion to the measuring distance. In the case of the measuring system using an interferometer, the distance to an object is measured based upon the OPD between a reference beam and a measuring (returning) beam. Thus, a reflector capable of reflecting the measuring beam should be attached to the object. That is, a space sensor according to this measuring system has drawbacks such as limited use and high price even though it can measure the object with a very high precision of, for example, several millimeters (mm).
Conversely, a sensor according to the TOF technology can calculate the distance to an object in a relatively simple fashion by detecting a pulse dispersing from the object even if a specific device is not attached to the object. As advantages, the TOF sensor can easily measure a long distance without spatial limitations. However, the TOF technology calculates the distance based on the time difference, obtained by measuring the reflecting pulse, and thus requires a high efficiency optical system, which can detect a faint pulse dispersing and returning from an object.
Accordingly, it is required to develop an approach to raise responsivity in the TOF sensor, which has a simple structure and is widely applicable.